The connection.info dictionary comes from the underlying
pooled connection, which in a disconnection situation
is not there; trying to access it makes it try to reconnect.
Inside of rollback(), SQLAlchemy doesn't allow us to
reconnect yet because we haven't finished removing the
transctional state that corresponds to the now-discarded
connection. Therefore we have to check connection.invalidated
inside of our rollback handlers before trying to add/remove tokens
from connection.info.
Change-Id: Icd10ada68d6d53410ac88eca3577f04c5e30087e
Resolves-bug: #1704474
7c5b7d3e03